Hervé
5th May 2016, 18:06
Although the article bellow is from the alarmist Daily Mail repeater it has the best graphics :)
The south is SINKING: Giant chunks of the Earth's mantle are falling off and causing quakes across the southeastern US - and more are coming, warn researchers (http://www.dailymail.co.uk/sciencetech/article-3573759/Giant-chunks-Earth-s-mantle-FALLING-causing-quakes-southeastern-coming-warn-researchers.html)
Area hit by a series of strange unexplained quakes
Most recent was 2011 magnitude-5.8 earthquake near Mineral, Virginia
Area should be seismically quiet as it is in middle of Earth's tectonic plate
By Mark Prigg For Dailymail.com (http://www.dailymail.co.uk/home/search.html?s=&authornamef=Mark+Prigg+For+Dailymail.com)
Published: 18:23 GMT, 4 May 2016 |
Updated: 00:44 GMT, 5 May 2016
The southeastern United States has been hit by a series of strange unexplained quakes - most recently, the 2011 magnitude-5.8 earthquake near Mineral, Virginia that shook the nation's capital.
Researchers have been baffled, believing the areas should be relatively quiet in terms of seismic activity, as it is located in the interior of the North American Plate, far away from plate boundaries where earthquakes usually occur.
Now, they believe the quakes could be caused by pieces of the Earth's mantle breaking off and sinking into the planet.
http://i.dailymail.co.uk/i/pix/2016/05/04/21/33D84AE400000578-3573759-image-m-3_1462394830633.jpg
This map shows the study area in detail, showing various tectonic attributes of the Southeastern United States.
BMA = BrunswickMagnetic Anomaly, BRE = Blue Ridge Escarpment,
CFA = Cape Fear Arch, OS = Orangeburg Scarp
ETSZ = EasternTennessee Seismic Zone
NMSZ = New Madrid Seismic Zone
GCSZ = Giles County Seismic Zone,
SCSZ = South Carolina Seismic Zone
CVSZ = Central Virginia Seismic Zone
V1 = Eocene Virginia Volcanics,
V2 = Jackson, Mississippi Volcanism,
V3 = Offshore Louisiana Volcanism.
Seismicity is from the Virginia Tech Seismological Observatory catalog (1900–2014).
Researchers believe the quakes could be caused by pieces of the Earth's mantle breaking off and sinking into the planet in the affected area (shown here). They say pieces of the mantle have most likely been breaking off from underneath the plate since at least 65 million years ago. This map shows the study area in detail.
A new study found pieces of the mantle under this region have been periodically breaking off and sinking down into the Earth.
This thins and weakens the remaining plate, making it more prone to slipping that causes earthquakes.
The study authors conclude this process is ongoing and likely to produce more earthquakes in the future.
'Our idea supports the view that this seismicity will continue due to unbalanced stresses in the plate,' said Berk Biryol, a seismologist at the University of North Carolina at Chapel Hill and lead author of the new study.
'The [seismic] zones that are active will continue to be active for some time.'
The study was published in the Journal of Geophysical Research – Solid Earth, a journal of the American Geophysical Union.
'Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere,' the team wrote.
Compared to earthquakes near plate boundaries, earthquakes in the middle of plates are not well understood and the hazards they pose are difficult to quantify.
http://i.dailymail.co.uk/i/pix/2016/05/04/19/33D7962200000578-3573759-image-a-2_1462385643709.jpg
The new findings could help scientists better understand the dangers these earthquakes present.
Today, the southeastern U.S. is more than 1,056 miles from the nearest edge of the North American Plate, which covers all of North America, Greenland and parts of the Atlantic and Arctic oceans.
But the region was built over the past billion years by periods of accretion, when new material is added to a plate, and rifting, when plates split apart.
Researchers initially suspected ancient fault lines or pieces of old plates extending deep in the mantle following episodes of accretion and rifting could be responsible for earthquakes in the area.
'This region has not been active for a long time,' Biryol said.
WHAT ARE TECTONIC PLATES?
Tectonic plates are composed of Earth's crust and the uppermost portion of the mantle.
Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.
http://i.dailymail.co.uk/i/pix/2016/05/04/21/33D85C1400000578-3573759-image-a-2_1462394779758.jpg
The world's tectonic plates: Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other.
Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate.
These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.'We were intrigued by what was going on and how we can link these activities to structures in deeper parts of the Earth.'
'This was an interesting finding because everybody thought that this is a stable region, and we would expect regular plate thickness,' Biryol said.
At first, they thought the thick, old rocks could be remnants of ancient tectonic plates.
http://i.dailymail.co.uk/i/pix/2016/05/04/19/33D7961200000578-3573759-Shaking_from_the_magnitude_5_8_earthquake_near_Mineral_Virginia_-m-8_1462385724641.jpg
Shaking from the magnitude 5.8 earthquake near Mineral, Virginia on August 23, 2011 was felt by more people than any other earthquake in U.S. history, according to the U.S. Geological Survey. Researchers now believe the quakes could be caused by pieces of the Earth's mantle breaking off and sinking into the planet.
But the shapes and locations of the thick and thin regions suggested a different explanation: through past rifting and accretion, areas of the North American Plate have become more dense and were pulled downward into the mantle through gravity.
At certain times, the densest parts broke off from the plate and sank into the warm asthenosphere below.
The asthenosphere, being lighter and more buoyant, surged in to fill the void created by the missing pieces of mantle, eventually cooling to become the thin, young rock in the images.
http://i.dailymail.co.uk/i/pix/2016/05/04/19/33D7961A00000578-3573759-image-a-4_1462385658607.jpg
Volcanoes were once active in the southeastern. U.S. Mole Hill, pictured here, is a mound of volcanic rock in the Shenandoah Valley in Virginia that formed from an active volcano 48 million years ago (a relatively recent event, in geological time scales).
The researchers concluded this process is likely what causes earthquakes in this otherwise stable region: when the pieces of the mantle break off, the plate above them becomes thinner and more prone to slip along ancient fault lines.
Typically, the thicker the plate, the stronger it is, and the less likely to produce earthquakes.
According to Biryol, pieces of the mantle have most likely been breaking off from underneath the plate since at least 65 million years ago.
Because the researchers found fragments of hard rocks at shallow depths, this process is still ongoing and likely to continue into the future, potentially leading to more earthquakes in the region, he said.
HOW THEY LOOKED INSIDE THE EARTH
https://upload.wikimedia.org/wikipedia/commons/thumb/d/d6/NorthAmericanPlate.png/956px-NorthAmericanPlate.png
A map of the North American Plate (https://en.wikipedia.org/wiki/North_American_Plate). Arrows show directions of its movement across Earth's surface. Numbers refer to millimetres/year displacement with respect to the African plate
To find out what was happening deep below the surface, the researchers created 3D images of the mantle portion of the North American Plate.
Just as doctors image internal organs by tracing the paths of x-rays through human bodies, seismologists image the interior of the Earth by tracing the paths of seismic waves created by earthquakes as they move through the ground.
These waves travel faster through colder, stiffer, denser rocks and slower through warmer, more elastic rocks.
Rocks cool and harden as they age, so the faster seismic waves travel, the older the rocks.
The researchers used tremors caused by earthquakes more than 2,200 miles away to create a 3D map of the mantle underlying the U.S. east of the Mississippi River and south of the Ohio River.
They found plate thickness in the southeast U.S. to be fairly uneven – they saw thick areas of dense, older rock stretching downward and thin areas of less dense, younger rock.Original article: http://onlinelibrary.wiley.com/doi/10.1002/2015JB012698/abstract
Simplified version: http://blogs.agu.org/geospace/2016/05/03/scientists-find-likely-cause-recent-southeast-u-s-earthquakes/
The south is SINKING: Giant chunks of the Earth's mantle are falling off and causing quakes across the southeastern US - and more are coming, warn researchers (http://www.dailymail.co.uk/sciencetech/article-3573759/Giant-chunks-Earth-s-mantle-FALLING-causing-quakes-southeastern-coming-warn-researchers.html)
Area hit by a series of strange unexplained quakes
Most recent was 2011 magnitude-5.8 earthquake near Mineral, Virginia
Area should be seismically quiet as it is in middle of Earth's tectonic plate
By Mark Prigg For Dailymail.com (http://www.dailymail.co.uk/home/search.html?s=&authornamef=Mark+Prigg+For+Dailymail.com)
Published: 18:23 GMT, 4 May 2016 |
Updated: 00:44 GMT, 5 May 2016
The southeastern United States has been hit by a series of strange unexplained quakes - most recently, the 2011 magnitude-5.8 earthquake near Mineral, Virginia that shook the nation's capital.
Researchers have been baffled, believing the areas should be relatively quiet in terms of seismic activity, as it is located in the interior of the North American Plate, far away from plate boundaries where earthquakes usually occur.
Now, they believe the quakes could be caused by pieces of the Earth's mantle breaking off and sinking into the planet.
http://i.dailymail.co.uk/i/pix/2016/05/04/21/33D84AE400000578-3573759-image-m-3_1462394830633.jpg
This map shows the study area in detail, showing various tectonic attributes of the Southeastern United States.
BMA = BrunswickMagnetic Anomaly, BRE = Blue Ridge Escarpment,
CFA = Cape Fear Arch, OS = Orangeburg Scarp
ETSZ = EasternTennessee Seismic Zone
NMSZ = New Madrid Seismic Zone
GCSZ = Giles County Seismic Zone,
SCSZ = South Carolina Seismic Zone
CVSZ = Central Virginia Seismic Zone
V1 = Eocene Virginia Volcanics,
V2 = Jackson, Mississippi Volcanism,
V3 = Offshore Louisiana Volcanism.
Seismicity is from the Virginia Tech Seismological Observatory catalog (1900–2014).
Researchers believe the quakes could be caused by pieces of the Earth's mantle breaking off and sinking into the planet in the affected area (shown here). They say pieces of the mantle have most likely been breaking off from underneath the plate since at least 65 million years ago. This map shows the study area in detail.
A new study found pieces of the mantle under this region have been periodically breaking off and sinking down into the Earth.
This thins and weakens the remaining plate, making it more prone to slipping that causes earthquakes.
The study authors conclude this process is ongoing and likely to produce more earthquakes in the future.
'Our idea supports the view that this seismicity will continue due to unbalanced stresses in the plate,' said Berk Biryol, a seismologist at the University of North Carolina at Chapel Hill and lead author of the new study.
'The [seismic] zones that are active will continue to be active for some time.'
The study was published in the Journal of Geophysical Research – Solid Earth, a journal of the American Geophysical Union.
'Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere,' the team wrote.
Compared to earthquakes near plate boundaries, earthquakes in the middle of plates are not well understood and the hazards they pose are difficult to quantify.
http://i.dailymail.co.uk/i/pix/2016/05/04/19/33D7962200000578-3573759-image-a-2_1462385643709.jpg
The new findings could help scientists better understand the dangers these earthquakes present.
Today, the southeastern U.S. is more than 1,056 miles from the nearest edge of the North American Plate, which covers all of North America, Greenland and parts of the Atlantic and Arctic oceans.
But the region was built over the past billion years by periods of accretion, when new material is added to a plate, and rifting, when plates split apart.
Researchers initially suspected ancient fault lines or pieces of old plates extending deep in the mantle following episodes of accretion and rifting could be responsible for earthquakes in the area.
'This region has not been active for a long time,' Biryol said.
WHAT ARE TECTONIC PLATES?
Tectonic plates are composed of Earth's crust and the uppermost portion of the mantle.
Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.
http://i.dailymail.co.uk/i/pix/2016/05/04/21/33D85C1400000578-3573759-image-a-2_1462394779758.jpg
The world's tectonic plates: Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other.
Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate.
These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.'We were intrigued by what was going on and how we can link these activities to structures in deeper parts of the Earth.'
'This was an interesting finding because everybody thought that this is a stable region, and we would expect regular plate thickness,' Biryol said.
At first, they thought the thick, old rocks could be remnants of ancient tectonic plates.
http://i.dailymail.co.uk/i/pix/2016/05/04/19/33D7961200000578-3573759-Shaking_from_the_magnitude_5_8_earthquake_near_Mineral_Virginia_-m-8_1462385724641.jpg
Shaking from the magnitude 5.8 earthquake near Mineral, Virginia on August 23, 2011 was felt by more people than any other earthquake in U.S. history, according to the U.S. Geological Survey. Researchers now believe the quakes could be caused by pieces of the Earth's mantle breaking off and sinking into the planet.
But the shapes and locations of the thick and thin regions suggested a different explanation: through past rifting and accretion, areas of the North American Plate have become more dense and were pulled downward into the mantle through gravity.
At certain times, the densest parts broke off from the plate and sank into the warm asthenosphere below.
The asthenosphere, being lighter and more buoyant, surged in to fill the void created by the missing pieces of mantle, eventually cooling to become the thin, young rock in the images.
http://i.dailymail.co.uk/i/pix/2016/05/04/19/33D7961A00000578-3573759-image-a-4_1462385658607.jpg
Volcanoes were once active in the southeastern. U.S. Mole Hill, pictured here, is a mound of volcanic rock in the Shenandoah Valley in Virginia that formed from an active volcano 48 million years ago (a relatively recent event, in geological time scales).
The researchers concluded this process is likely what causes earthquakes in this otherwise stable region: when the pieces of the mantle break off, the plate above them becomes thinner and more prone to slip along ancient fault lines.
Typically, the thicker the plate, the stronger it is, and the less likely to produce earthquakes.
According to Biryol, pieces of the mantle have most likely been breaking off from underneath the plate since at least 65 million years ago.
Because the researchers found fragments of hard rocks at shallow depths, this process is still ongoing and likely to continue into the future, potentially leading to more earthquakes in the region, he said.
HOW THEY LOOKED INSIDE THE EARTH
https://upload.wikimedia.org/wikipedia/commons/thumb/d/d6/NorthAmericanPlate.png/956px-NorthAmericanPlate.png
A map of the North American Plate (https://en.wikipedia.org/wiki/North_American_Plate). Arrows show directions of its movement across Earth's surface. Numbers refer to millimetres/year displacement with respect to the African plate
To find out what was happening deep below the surface, the researchers created 3D images of the mantle portion of the North American Plate.
Just as doctors image internal organs by tracing the paths of x-rays through human bodies, seismologists image the interior of the Earth by tracing the paths of seismic waves created by earthquakes as they move through the ground.
These waves travel faster through colder, stiffer, denser rocks and slower through warmer, more elastic rocks.
Rocks cool and harden as they age, so the faster seismic waves travel, the older the rocks.
The researchers used tremors caused by earthquakes more than 2,200 miles away to create a 3D map of the mantle underlying the U.S. east of the Mississippi River and south of the Ohio River.
They found plate thickness in the southeast U.S. to be fairly uneven – they saw thick areas of dense, older rock stretching downward and thin areas of less dense, younger rock.Original article: http://onlinelibrary.wiley.com/doi/10.1002/2015JB012698/abstract
Simplified version: http://blogs.agu.org/geospace/2016/05/03/scientists-find-likely-cause-recent-southeast-u-s-earthquakes/